Interpretive Summary: Beneficial nematodes (also known as entomopathogenic nematodes) are environmentally friendly bio-insecticides. These nematodes can control a wide variety of economically important insect pests. However, sensitivity to freezing or desiccating (drying out) reduces the nematodes’ survival and therefore can limit their utility as biological control agents. Therefore, it is important to determine which nematode species and strains are most tolerant to adverse conditions such as freezing and desiccation. We measured freezing and desiccation tolerance in a wide variety of nematode species and strains. We discovered that certain species or strains are much more tolerant than others. For example, the nematode species called Steinernema carpocapsae, Steinernema feltiae and Steinernema rarum were among the most desiccation tolerant, and Steinernema feltiae and Heterorhabditis georgiana were among the more freeze tolerant nematodes. These findings will assist researchers, farmers, and pest control applicators in choosing which nematode to use when dry or freezing conditions may be present.

Technical Abstract:
The ability of entomopathogenic nematodes to tolerate environmental stress such as desiccating or freezing conditions, can contribute significantly to biocontrol efficacy. Our objective was to compare inter and intraspecific variation in freeze and desiccation tolerance among a broad array of entomopathogenic nematodes. In laboratory studies we compared nematodes at two levels of relative humidity and exposure periods and nematodes were exposed to freezing temperatures for 6 or 24 h. To assess interspecific variation we compared 10 species including: Heterorhabditis bacteriophora (VS), H. floridensis, H. georgiana, (Kesha), H. indica (HOM1), H. megidis (UK211), Steinernema carpocapsae (All), S. feltiae (SN), S. glaseri (VS), S. rarum (17C&E), and S. riobrave (355). To assess intraspecific variation we compared five strains of H. bacteriophora (Baine, Fl11, Hb, Oswego, and VS) and four strains of S. carpocapsae (All, Cxrd, DD136, and Sal), and S. riobrave (355, 38b, 7-12, and TP). S. carpocapsae exhibited the highest level of desiccation tolerance among species followed by S. feltiae and S. rarum; the heterorhabditid species exhibited the least desiccation tolerance and S. riobrave and S. glaseri were intermediate. No intraspecific variation was observed in desiccation tolerance; S. carpocapsae strains showed higher tolerance than all H. bacteriophora or S. riobrave strains yet there was no differences detected within species. In interspecies comparisons, poor freeze tolerance was observed in H. indica, and S. glaseri, S. rarum and S. riobrave whereas H. georgiana and S. feltiae exhibited the highest freeze tolerance, particularly in the 24 h exposure period. Unlike desiccation tolerance, substantial intraspecies variation in freeze tolerance was observed among H. bacteriophora and S. riobrave strains, yet within species variation was not detected among S. carpocapsae strains. Correlation analysis did not detect a relationship between freezing and desiccation tolerance.